Reimplement isPotentiallyReachable to make nocapture deduction much stronger.

Adds unit tests for it too.

Split BasicBlockUtils into an analysis-half and a transforms-half, and put the
analysis bits into a new Analysis/CFG.{h,cpp}. Promote isPotentiallyReachable
into llvm::isPotentiallyReachable and move it into Analysis/CFG.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187283 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 69 insertions, 22 deletions

diff --git a/include/llvm/Analysis/CFG.h b/include/llvm/Analysis/CFG.h
new file mode 100644
index 0000000..08fdc26
--- /dev/null
+++ b/include/llvm/Analysis/CFG.h
@@ -0,0 +1,69 @@
+//===-- Analysis/CFG.h - BasicBlock Analyses --------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This family of functions performs analyses on basic blocks, and instructions
+// contained within basic blocks.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_CFG_H
+#define LLVM_ANALYSIS_CFG_H
+
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/Support/CFG.h"
+
+namespace llvm {
+
+class BasicBlock;
+class DominatorTree;
+class Function;
+class Instruction;
+class LoopInfo;
+class TerminatorInst;
+
+/// Analyze the specified function to find all of the loop backedges in the
+/// function and return them.  This is a relatively cheap (compared to
+/// computing dominators and loop info) analysis.
+///
+/// The output is added to Result, as pairs of <from,to> edge info.
+void FindFunctionBackedges(
+    const Function &F,
+    SmallVectorImpl<std::pair<const BasicBlock *, const BasicBlock *> > &
+        Result);
+
+/// Search for the specified successor of basic block BB and return its position
+/// in the terminator instruction's list of successors.  It is an error to call
+/// this with a block that is not a successor.
+unsigned GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ);
+
+/// Return true if the specified edge is a critical edge. Critical edges are
+/// edges from a block with multiple successors to a block with multiple
+/// predecessors.
+///
+bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
+                    bool AllowIdenticalEdges = false);
+
+/// Determine whether there is a path from From to To within a single function.
+/// Returns false only if we can prove that once 'From' has been executed then
+/// 'To' can not be executed. Conservatively returns true.
+///
+/// This function is linear with respect to the number of blocks in the CFG,
+/// walking down successors from From to reach To, with a fixed threshold.
+/// Using DT or LI allows us to answer more quickly. LI reduces the cost of
+/// an entire loop of any number of blocsk to be the same as the cost of a
+/// single block. DT reduces the cost by allowing the search to terminate when
+/// we find a block that dominates the block containing 'To'. DT is most useful
+/// on branchy code but not loops, and LI is most useful on code with loops but
+/// does not help on branchy code outside loops.
+bool isPotentiallyReachable(const Instruction *From, const Instruction *To,
+                            DominatorTree *DT = 0, LoopInfo *LI = 0);
+
+} // End llvm namespace
+
+#endif
diff --git a/include/llvm/Transforms/Utils/BasicBlockUtils.h b/include/llvm/Transforms/Utils/BasicBlockUtils.h
index 8f1a6e2..b5478cb 100644
--- a/include/llvm/Transforms/Utils/BasicBlockUtils.h
+++ b/include/llvm/Transforms/Utils/BasicBlockUtils.h
@@ -70,28 +70,6 @@ void ReplaceInstWithInst(BasicBlock::InstListType &BIL,
 //
 void ReplaceInstWithInst(Instruction *From, Instruction *To);
 
-/// FindFunctionBackedges - Analyze the specified function to find all of the
-/// loop backedges in the function and return them.  This is a relatively cheap
-/// (compared to computing dominators and loop info) analysis.
-///
-/// The output is added to Result, as pairs of <from,to> edge info.
-void FindFunctionBackedges(const Function &F,
-      SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result);
-
-
-/// GetSuccessorNumber - Search for the specified successor of basic block BB
-/// and return its position in the terminator instruction's list of
-/// successors.  It is an error to call this with a block that is not a
-/// successor.
-unsigned GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ);
-
-/// isCriticalEdge - Return true if the specified edge is a critical edge.
-/// Critical edges are edges from a block with multiple successors to a block
-/// with multiple predecessors.
-///
-bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
-                    bool AllowIdenticalEdges = false);
-
 /// SplitCriticalEdge - If this edge is a critical edge, insert a new node to
 /// split the critical edge.  This will update DominatorTree and
 /// DominatorFrontier information if it is available, thus calling this pass